As the state moves to takeover the Dever Elementary School in Dorchester, many teachers and parents are protesting a plan to scrap a popular program that aims to make students fluent in both English and Spanish.

State officials say the dual-language program played a major role in the Dever’s persistently low test scores that caused it to slide into receivership and they believe that an English-only approach to instruction is the best way to boost achievement.

The recommendation delivers a setback for the Boston school system as it prepares a major expansion of dual-language schools to accommodate demand by families who are either native speakers of English or another language. It also is rekindling a debate about the extent to which a language other than English should be used in the teaching of math, science, and other academic subjects.

“I don’t think [the dual-language program] is salvageable at this point,” Mitchell Chester, state commissioner of elementary and secondary education, said in an interview. “We saw no evidence that the dual language or traditional program were delivering results. Both were coming up short.”

Teachers and parents strongly disagree. They say the state is relying too heavily on MCAS results and is ignoring other data that show the program is yielding gains in the early grades, which are not subject to MCAS testing.

They plan to file a formal protest by Monday, the deadline for interested parties to respond to the commissioner’s plan.

Ellis said she is planning to withdraw her son, a kindergartner, from the Dever and is hoping to enroll him in another dual-language school. But she added that seats seldom open up there.

Dual-language schools are one of the few places where immigrant students have an opportunity to take classes in their native language, since state voters passed a referendum in 2002 that requires instruction to be taught predominantly in English.

The schools also attract many native English-speaking parents who want their children to learn another language and embrace a multicultural society.

Boston has only four such schools and for years parents and advocates have been clamoring for more. They finally scored a victory last year when the School Committee promised to add nine dual-language programs.

The first one opens this fall at the Umana Academy in East Boston, which like the other Boston schools, will teach in English and Spanish. The School Department hopes that future programs will tap other languages, such as Mandarin.

Interim Superintendent John McDonough said that while the Dever’s experience with dual-language was disappointing, he voiced confidence that similar endeavors at other schools would be more successful. McDonough said the school system established a rigorous process last year to review proposals to ensure quality.

“I do not want students to be participating in a program that provides an expectation to families that is not being met,” McDonough said.

Establishing a dual-language program takes years, typically starting with kindergartners and subsequently adding grade levels as students advance. Consequently, it can take five or six years for schools to see results.

Dever started its program five years ago in the early grades. Teachers pushed the initiative because they believed it would boost the achievement of English-language learners and would be a draw for English-speaking families, as well.

The Dever was aggressively expanding the program to encapsulate all classrooms and grade levels and its nearly 600 students. Teachers spent countless hours after school and over weekends writing their own curriculums and translating instructional materials into Spanish, according to a state report this year on the Dever’s overhaul, which the state’s appointed receiver, Blueprint Schools Network, helped to prepare.

But state education officials said the school struggled to hire teachers who could teach in both languages and failed to provide enough teacher training.

The state review found inconsistent instruction among the classrooms and in many cases learning materials below grade level in both languages.

On last year’s MCAS, only 14 percent of Dever students were proficient or advanced in reading while 31 percent scored at those levels in math.

“The program is not functioning at a level that is likely to produce rapid academic growth that Dever students need and deserve.” the report concluded.

Richard Stutman, president of the Boston Teachers Union, said he expects most, if not all, teachers will leave the Dever after this school year.

“To say the dual-language program is holding back test score growth, I think, is really a disservice to the children,” Stutman said.

The School Department does not yet know how many students will leave the Dever, but has been meeting with parents to discuss transfer options and giving their children priority to enroll at other dual-language schools. Parent leaders say many parents plan to leave.

Roger Rice of Multicultural Education, Training & Advocacy, an organization that works on behalf of linguistic minorities, said the commissioner’s decision to dismantle the dual-language program was the kind of action he would expect in states such as Alabama and Arizona.

“I feel like it’s a really bad, intellectually bankrupt, tone-deaf decision,” Rice said. “Do you have to kill a program because you don’t know how to make it better?”

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